Multiple element, digital-to-analog converters (referred to herein as “multi-bit DACs”) may be found in the feed-forward paths of delta-sigma digital-to-analog converters, the feedback paths of delta-sigma analog-to-digital converters, and in other types of circuitry. A typical multi-bit DAC includes a plurality of DAC elements, arranged in parallel with each other. Each DAC element is adapted to receive one bit of an encoded input signal and to produce an analog output signal that has one of two levels, depending on the input bit. Because each DAC element is used to process a single bit, the elements often are referred to as “single-bit” DAC elements. The analog output signals from the plurality of single-bit DAC elements are summed together to produce a differential, analog output signal.
Very large scale integration (VLSI) processing techniques are generally used to implement multiple-bit DACs. Accordingly, mismatches inherently are present in corresponding components of the plurality of single-bit DAC elements. Left uncompensated for, these mismatches may introduce significant conversion noise in the output signal, thus detrimentally affecting the signal-to-noise ratio (SNR) of the output signal. In order to reduce the conversion noise, some multi-bit DAC architectures perform spectral shaping of the static mismatch inherent in the single-bit DAC elements, although at the cost of higher switching activity. When dynamic mismatches also are present (e.g., rise/fall time variations), their effects tend to be amplified by the higher switching activity introduced by the spectral shaping process. In addition, because the output signals from each of the single-bit DAC elements contribute to the differential output signal of the multi-bit DAC, regardless of the value of the input bit, each of the single-bit DAC elements contributes noise to the signal path. This also has a detrimental effect on the SNR of the output signal. Accordingly, what are needed are multi-bit DACs and conversion methods that may have improved SNR performance over traditional multi-bit DACs.